A piezoelectric drive element in which a ceramic piezoelectric oscillator is retained in an oscillator holding device and the oscillator holding device itself is mounted so as to be movable on guide rails inside a housing is known from DE 196 48 726 A1. The oscillator is pressed against an element that is to be driven via a spring, the construction of the device being such that the oscillator is able to move in the direction of the driven element, but movement in both directions perpendicular thereto is to be prevented as far as possible. In this context, the guide rails allow the oscillator and the oscillator holding device almost complete freedom of movement in the direction of the driven element (x-direction), but they are intended to prevent undesirable movement thereof in the direction of the housing (y-direction) and perpendicularly thereto (z-direction). Aligning or adjusting screws arranged on one side of the housing are intended to assist with the adjustment of the complex guidance structure.
The adjustment operation also requires a great deal of time and experience, since incorrect or inaccurate positioning of the adjusting screws can cause the housing to be bent out of shape, which in turn has a negative effect on the movability of the oscillator and oscillator holding device in the x-direction. If the housing is bent out of shape, the position of the guide rails too is shifted correspondingly, and smooth movement of the oscillator holding device inside the guide rails is rendered practically impossible. However, smooth movement of the oscillator holding device is essential for the proper functioning of the ultrasonic motor.
A further drawback associated with DE 196 48 726 A1 is that considerable effort is required at the manufacturing stage to effectively prevent movement of the oscillator holding device and thus also of the oscillator in the z-direction. Only with correspondingly tight dimensional tolerances in terms of the guide structure is it possible to ensure that movement in the z-direction is effectively prevented. On the other hand, given that the tolerances are so close, even the slightest deformations of the housing and the consequent changes in position of the guide rails will obstruct movement in the x-direction.
The preceding is intended to illustrate that the adjustment by means of the aligning or adjusting screws is of essential importance in the case of DE 196 48 726 A1, and is correspondingly time-consuming and expensive.